The objective of this research is the development and utilization of assays to detect the presence of 0.5 to 1% leukemic cells in the total nucleated bone marrow cell population by utilizing the differential rate of synthesis of the template independent DNA polymerase terminal deoxynucleotidyl transferase (TdT). Rather than utilizing the already well-characterized steady-state measurements embodied in biochemical, immunofluorescent, and antibody affinity assays, the dynamic quality of rate of TdT biosynthesis will be utilized to discriminate between normal and leukemic TdT-positive marrow populations. The biosynthesis rate by leukemic cells is measureably greater than the rate of synthesis by equivalent numbers of normal TdT positive cells in bone marrow. As a further refinement, cDNA probes for TdT-specific message will be utilized in model studies to establish correlations between rates of RNA synthesis, steady-state levels of mRNA, and protein biosynthesis. These measurements will be extended to heterogeneous model populations and, ultimately, clinical samples. The prognostic value of these assays will be determined by applying the assays to routine clinical samples from leukemia patients in treatment, or off treatment and in remission, who have had, or might develop, TdT positive disease.